I'm currently working for the first time with cable stitches and I'm knitting a hat in the round from a pattern. The pattern called for 70 CO stitches but I needed the extra room so I CO 80 instead. Now that I've reached the decrease rounds, of course numbers dont match up. The pattern Ive been using for the hat is a basic 6 stitch front twist cable stitch and 4 purls *slip 3, k3, k3, p4* all the way around for 80 stitches. Then 5 rows of following the knits and purls before I cable again.
For 70 CO stitches the pattern decreases as follows:
Rnd 1: *K6, P2tog, P2*, rep to end (63 sts)
Rnd 2: *K4, K2tog, P3*, rep to end (56 sts)
Rnd 3: *K5, P2tog, P1*, rep to end (49 sts)
Rnd 4: *K3, K2tog, P2*, rep to end (42 sts)...ect

But I need help with the row that would have come before for it for 80 stitches, because I have no Idea what the math would be. Aaaah Can someone help?

If you're using the same set of 6knits and 4 purls, you'll have one extra set when you cast on 80 instead of 70sts. Why not follow the same pattern of decreases around (with the one additional set) and make up the extra sts towards the very top of the hat, maybe k2tog all around before finishing off?